The purpose of this research is to find out what conformational changes are possible in chromatin. Although we will use other techniques, we will primarily use steady-state fluorescence anisotropy and fluorescence time decay. We have shown that tyrosin fluorescence anistropy is very sensitive to conformational changes in nucleosome core particles and will take advantage of this sensitivity to study transitions in other chromatin preparations and to study the binding of important chromosomal proteins to nucleosomes and chromatin. Two of the proteins that we will examine are HMG14 and HMG17, which bind to nucleosomes and have been found to be associated with structurally active chromatin. Studies of tyrosine anistropy have important advantages over other methods which are used to study this problem. The tyrosine residues are located naturally within the core of the nucleosome; there is no need for an extrinsic probe. Also, tyrosine anisotropy measuremens are fast and easy, and may be made equally well on very different preparations from core particles to oligomers, to chromatin itself. We have recently discovered that the fluorescence from Hl and from nucleosome core particles contains tyrosinate emission, presumably arising from excited state proton transfer from the tyrosine hydroxyl group. We will look for tyrosinate emission from the inner histones and other chromatin preparations. This excited state proton transfer is also sensitive to conformational changes and we will use it to study chromatin transitions. We will use our picosecond laser system with out fluorescence lifetime apparatus to measure the fluorescence decays from histones and chromatin. By examining both the lifetimes and the decay of the anisotropy using both intrinsic tyrosine and other extrinsic probes, we will learn more about the conformational changes and the molecular motions of the chromatin. These motions include restricted roation, macromolecular flexibilities and rotational diffusion.